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Standard Aquarium Sizes: Dimensions, Capacities and Weights

There’s several ways to choose the ideal aquarium, but before you settle on a particular tank there’s a few basic calculations you’ll want to check. The advantage of going with standard aquarium sizes over a custom design is the ease of determining the aquarium’s dimensions and weight, so let’s take a deeper look at these tanks!

Guide to Standard Aquarium Sizes

The modern loft interior with aquarium. 3d concept

If you’ve shopped around for aquariums in the last few years, you may have noticed that there’s a lot of options when it comes to modern tank styles and designs. This is a big change from the past when we only had the choice between standard size aquariums or shelling out the big bucks for a custom tank. 

These days, the main advantage of choosing a standard-sized aquarium over a unique design is you can easily look up and compare their dimensions, capacities and most importantly, estimate how much the filled tank will weigh. This spares you from having to use an aquarium calculator or doing the math by hand.

What Are Standard Aquariums?

Standard aquariums are the classic rectangular glass tanks that are sealed with silicone and have a plastic base and rim for extra support. These tanks are made from glass that’s usually 0.375 to 0.5 inches thick, and larger standards over 40-gallons have additional support rails across the center of the aquarium.

Vector of rectangular aquarium with dimensional signs.

Standard tanks are measured externally across the plastic base. Measurements may vary slightly across brands without altering their basic specs. For instance, all standard 10-gallon tanks have approximately the same dimensions (20 x 10 x 12 inches) and weigh about 111 pounds when filled with gravel and water.

It’s very easy to compare standard tanks by looking at a table, like the ones we’ve provided below. It’s harder to compare aquariums when you’re looking at a rimless, bow front or other non-standard sizes like hexagon fish tanks, and you’ll likely need to play with those pesky calculators and make your own aquarium size charts.

Standard Tank Sizes in the US

Let’s compare the specs between a wide range of standard tank sizes, from small Nano aquariums to the big behemoths that weigh over a ton when filled. Unlike the rest of the world, aquariums in the US are rated by their capacity in gallons of water instead of liters.

Small Aquariums 

Small Meadow Aquascape
Image Source : flickr.com

Small aquariums range in capacity from 2.5 to 15 gallons of water, and many can easily fit on a desk or sturdy table, so you may not need to invest in an aquarium stand. While these sizes are popular with beginners, it’s actually much harder to care for a small tank. Things can quickly go sideways in these tiny set-ups.

Standard Aquarium
(US Gallons)

2.5 gallon

5 gallon

10 gallon “Leader”

15 gallon

15 gallon Tall

(L x W x H inches)

12 x 6 x 8

16 x 8 x 10

20 x 10 x 12

24 x 12 x 12

20 x 10 x 18

Empty Aquarium Weight

3 pounds

7 pounds

11 pounds

21 pounds

22 pounds

Filled Freshwater Weight 

27 pounds

62 pounds

111 pounds

170 pounds

170 pounds


Medium Aquariums

Aquarium with cichlids fish from lake malawi

The ideal capacity for a beginning fish keeper is a medium-size aquarium from 20 to 40 gallons. They are not terribly expensive to set-up, and with a robust filtration system and good aquarium maintenance, it’s easy to avoid problems. If you look at their filled weights, however, you can see that investing in a good stand is probably the way to go.

Standard Aquarium
(US Gallons)

20 gallon High

20 gallon Long

25 gallon

29 gallon

30 gallon Breeder

40 gallon Long

40 gallon Breeder

(L x W x H inches)

24 x 12 x 16

30 x 12 x 12

24 x 12 x 20

30 x 12 x 18

36 x 18 x 12

48 x 12 x 16

36 x 18 x 16

Empty Aquarium Weight

25 pounds

25 pounds

32 pounds

40 pounds

48 pounds

55 pounds

58 pounds

Filled Freshwater Weight 

225 pounds

225 pounds

282 pounds

330 pounds

384 pounds

455 pounds

458 pounds


Large Aquariums

Beautiful aquarium in the living room.

The biggest standard aquariums range from 50 to almost 200 gallons in capacity, and these large aquariums require a lot of thought and planning. You’ll definitely want to invest in a quality stand, perhaps with a matching hood, and you’ll likely need to measure the room to ensure you’ve space for equipment like filters, sumps, or chillers.

Standard Aquarium
(US Gallons)

50 gallon

55 gallon

65 gallon

75 gallon

90 gallon

125 gallon

150 gallon

180 gallon

(L x W x H inches)

36 x 18 x 19

48 x 13 x 21

36 x 18 x 24

48 x 18 x 21

48 x 18 x 24

72 x 18 x 21

72 x 18 x 28

72 x 24 x 25

Empty Aquarium Weight

100 pounds

78 pounds

126 pounds

140 pounds

160 pounds

206 pounds

338 pounds

430 pounds

Filled Freshwater Weight 

600 pounds

628 pounds

772 pounds

850 pounds

1050 pounds

1400 pounds

1800 pounds

2100 pounds


Extra Large Aquariums

The interior of the Oceanarium Crocus City, over 5000 species of fish and other animals from all over the world. Moscow, Russia

Once you start considering tanks bigger than 180 gallons, you really don’t have any standard options to choose from. Each manufacturer has their own unique extra-large models, often made from lighter materials like acrylic and with features like rounded corners and predrilled holes for chillers and sump filters. You’ll want to compare specific brands and models to find the best fit for your home.

How to Choose The Right Aquarium Size

There’s several factors you should consider before you settle on a tank size and style. It’s easier to maintain larger aquariums and they are a better choice for novice aquarists. If something goes wrong in a small capacity tank you may not catch things in time to prevent a crash.

Tank Size and Weight 

Obviously, you’ll want to choose a tank that physically fits in the location you’ve picked out for your aquarium. The dimensions of your tank directly impact its weight, and you shouldn’t assume that tanks with the same capacity will have the same filled weight, especially when comparing standard to non-standard designs.

For instance, you’ll notice that the two standard 40-gallon tanks differ in their empty and filled weight by a few pounds even with similar capacities. It’s better to overestimate your aquarium’s filled weight instead of risking a collapse. The bulk of your tank’s weight comes from the substrate/decor and the water it holds.


close up image of underwater landscape nature style aquarium tank with a variety of aquatic plants inside.

You’ll usually add about 1-pound of substrate per gallon of water, but this varies quite a bit. For compact options like sand and fine gravels, you’ll often have to use half-again or twice as much to get the coverage you need, especially for aquascaped and planted tanks. A standard planted 10-gallon can easily weigh over 120 pounds.

How Much Does a Gallon of Water Weigh?

The weight of a gallon of water varies a bit around the world, since it depends on the water’s density and how it’s measured. In the US, a gallon of water contains 3.785 liters, while the UK’s imperial gallon is the equivalent to 4.546 liters. So you’ll want to double-check your units of measurement to avoid making an error.

Freshwater is lighter than saltwater, and the exact weight of a gallon of water depends on the temperature, mineral content and salinity. Freshwater weighs about 8.345 pounds per gallon, and a gallon of saltwater is about 8.554 pounds.

Freshwater vs Saltwater Fish

You’ll also want to consider what kind of fish you’d like to keep and whether you’d prefer a freshwater or saltwater set-up. Your aquarium size and capacity will influence the types of animals you can keep and how many aquatic pets will fit harmoniously in your community.

Freshwater Fish Size Guide

Neon tetra fish with aquatic plant in aquarium

Freshwater aquariums are the best type for novices and beginners to start with, since they are easier to set-up and maintain. While the rule-of-thumb is to allow for at least 1-gallon of water per inch of fish in a freshwater aquarium, it just depends on the needs of each species:

  • Neon Tetras are only 1.5-inches in length, but they need at least a 10-gallon tank because they prefer to be kept in groups of 10 or more.
  • A group of three guppies, on the other hand, do just fine together in a 5-gallon tank.


Betta Fish

Common Goldfish

Fancy Goldfish

Neon Tetra


Average Size

2.5 to 5 inches

8 to 12 inches

6 to 8 inches

1.5 inches

1 to 2.5 inches

US Gallons
per Fish

2.5 to 5 gallons

20 to 30 gallons

15 to 20 gallons

1 to 2 gallons

1 to 2 gallons

Tank Size

2.5 to 5 gallons

20 gallons

15 gallons

10 gallons

5 gallons


Saltwater Fish Size Guide

The Marine Fish - Ocellaris clownfish

Saltwater tanks require a heftier investment in equipment like chillers, wavemakers and LED lights and are more complicated to establish and maintain. It’s usually best to get some fishkeeping experience before you dive into a saltwater set-up.

  • Saltwater fish require more care overall, since even topping off the water in the tank requires you to pay attention to your water’s salinity levels.
  • Depending on their size and activity levels, some saltwater fish need very roomy environments to remain healthy.
  • Saltwater fish are also more expensive to purchase, so stocking a tank can be a pricey endeavor. 


Clown Fish

Yellow Tang

Watchman Goby

Azure Damselfish

Purple Firefish

Average Size (length)

3 inches

8 inches

4 inches

2.5 inches

2.5 to 3.25 inches

Minimum Tank Size

30 gallons

100 gallons

30 gallons

30 gallons

10 gallons


Type of Aquatic Set-Up

Beautiful planted tropical freshwater aquarium with fishes. Aquascape.

The best size and shape for your aquarium also depends on how you’re planning to use it. Non-standard designs like tall portrait-style and cube-shaped tanks are attractive, but often a poor option for really active swimmers, like goldfish.

  • If you just need small tanks for a hospital or quarantine set-ups, a couple of standard 5 or 10-gallons may be ideal. They are compact but wide enough for fish to swim and you can swap equipment between tanks when needed.
  • Breeder tanks are a popular choice for medium-sized community aquariums, because their deep and shallow design allows for more surface area and better gas exchange.
  • Tall-style tanks are a great way to show-off a mixed community, and the additional height can help your mid-dwellers and surface fish stand out.


Standard aquariums make designing and setting up your tank a breeze, because you can easily look up their dimensions and estimate their filled weight without having to strain your brain with equations. What size aquarium did you choose, and did you go with a standard tank or a unique design? Share your comments below!

Jen has more than 30 years experience as a biologist, aquarist, and fishkeeper. She is an expert in setting up new tanks and maintaining naturally-planted freshwater habitats, and has experience raising a wide variety of aquatic species.

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